Authorities in New Hampshire say the search for Harmony Montgomery, who was last seen nearly three years ago, has become a murder investigation.

The last reported sighting of Harmony was in December 2019, when she was five years old. Police didn’t open a missing person’s investigation until December 2021, after she was reported missing by her mother, Crystal Sorey, who lost custody of her daughter in 2018.

Months of work on the case, by Manchester police, U.S. Marshalls and the FBI, have led authorities to conclude Harmony was killed in early December 2019, New Hampshire Attorney General John Formella said Thursday in a press release.

“At this point, while Harmony’s remains have not yet been located, we do have multiple sources of investigative information, including recently confirmed biological evidence that have led us to this difficult and tragic conclusion,” Formella said. “As a result, today I am announcing that this is now officially a homicide investigation and that our investigators will continue to seek justice and look into the circumstances of Harmony’s murder and search for her remains.”

Formella did not say whether police have identified any suspects in Harmony’s death. Citing the ongoing investigation, he said no information about the “specifics or nature of the evidence” would be released.

Harmony was in the custodial care of her father, Adam Montgomery, until January 4, when he was arrested for allegedly hitting the girl in the face. He was indicted on second-degree assault charges in March. Kayla Montgomery, Harmony’s stepmother, was indicted for fraud for allegedly collecting state support for Harmony for two years after she disappeared.

Formella said after the arrests that investigators had learned that Harmony disappeared shortly after she and her family were evicted from their home. Multiple people reported seeing Harmony with her father and Kayla Montgomery in the days after the eviction. But, according to police, the last reported sighting of Harmony was between Dec. 6 and Dec 10, 2019.

Formella said the department’s thoughts go out to Harmony’s family and asked anyone with information regarding Montgomery’s murder to contact the Manchester Police Department.